Replace vanilla HTML with React + shadcn/ui + TailwindCSS scaffold

- Frontend: React 19 + Vite + TypeScript + TailwindCSS v4 + shadcn/ui
- Pre-installed shadcn/ui components: Button, Card, Input, Separator
- Multi-stage Dockerfile: build React client → serve with Express
- Server.js updated to serve built React SPA with API routes
- Sample landing page with shadcn/ui components demonstrating usage
- Path aliases (@/) configured in tsconfig + vite config
- components.json for easy `shadcn add <component>` usage

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

client/tsconfig.tsbuildinfo

@@ -0,0 +1 @@
+{"root":["./src/App.tsx","./src/main.tsx","./src/vite-env.d.ts","./src/components/ui/button.tsx","./src/components/ui/card.tsx","./src/components/ui/input.tsx","./src/components/ui/separator.tsx","./src/lib/utils.ts","./src/pages/Home.tsx"],"version":"5.7.3"}